The three mineralized tissues of teeth are enamel, cementum and dentine. In human teeth, enamel covers the crown dentine whereas cementum covers the root dentine. In turn, the dentine encloses the pulp of the tooth which provides the dentine with vascular and neural support. Unlike enamel and cementum, the dentine is transversed by numerous tubules. The tubule walls are comprised of the calcified matrix of the dentine and the tubule space is filled with fluid (dentinal fluid) derived from pulp tissue fluid and serum. The matrix mineral is comprised mainly of the calcium phosphate salt, hydroxyapatite, which is poorly soluble at neutral and alkaline pH, and progressively more soluble as the pH becomes progressively more acidic.
Because of their rigid walls, the fluid that fills the narrow dentinal tubules enables cold, tactile, evaporative and osmotic stimuli to be transmitted through the dentine to the pulp in the form of fluid movement. This movement of dentinal fluid is sensed as sharp pain of short duration. This pain is elicited when the odontoblasts that protrude into the pulpal ends of the tubules are disturbed and as a result, the mechano-receptors of the pulpal nerve fibers attached thereto are stimulated. The neural response is usually referred to as dentinal pain and the involved dentine as hypersensitive dentine.
Dentinal hypersensitivity results when protective enamel or cementum covering dentine is lost. Cementum is easier to breach than enamel, because cementum is thinner and more easily eroded by acids. However, breach of cementum cannot happen until there is gingival recession and exposure of the root surface to the oral milieu. Individuals with breached cementum and suffering with dentinal hypersensitivity often experience pain when the exposed area of the tooth comes into contact with cold air or hot and cold liquids or foods that are sweet or acidic or is touched with a metal object.
One way that loss of cementum occurs (and the same is true of enamel) is by the process of dental caries. Acids are produced as end-products of the bacterial degradation of fermentable carbohydrate and these acids dissolve hydroxyapatite, which, like dentine and enamel, is the main calcium phosphate mineral that comprises most of the mineral of the cementum. Another source is acidic foods which, if ingested frequently and for prolonged periods of time, will cause tooth demineralization. These include fruit juices and many beverages, both alcoholic and non-alcoholic. Other acidic agents leading to chemical erosion include various oral personal care products. Amongst these are many of the commercially available mouthwashes and some toothpastes. Abrasive toothpastes and vigorous brushing can aid the erosion process. Another way in which dentinal tubules lose their protective cementum and enamel coverings is through procedures performed by the dentist or hygienist in the dental office. This includes cavity and crown preparation of teeth for fillings and other restorations. It also includes cementum removal during scaling and root planing by the periodontist or dental hygienist.
Many attempts have been made with limited success to plug exposed dentinal tubules and to thereby reduce or stop the ability of stimuli to reach the pulp and cause pain. Materials either singly or in combination have been tried to produce an effective plug. Blockage of the tubules through the formation of a calcium phosphate precipitate is a common approach. This includes the mixing of a soluble calcium salt with a soluble phosphate salt and immediately applying the combination to the open tubules. Alternatively, application of one salt before the other to try to get a precipitate to form within tubules is also used.
Substances other than calcium phosphate also have been utilized. For example, U.S. Pat. No. 3,683,006 describes using potassium, lithium or sodium nitrate. Another example is calcium oxalate particles of small and large size. Application of a protein denaturing agent, such as an alcohol, a surfactant, or a chaotropic salt, can also plug an exposed dentinal tubule since there is protein material within the dentinal tubules and denaturation can sometimes result in partial or complete tubule plugging. Still another but more drastic approach is to place a dental restoration in the affected area or cover the area with an adhesive material. U.S. Pat. No. 5,139,768 describes using a varnish containing strontium salt in a sustained hydrophobic polymer. Adherence without leakage of fluid from the tubules is not always easy to accomplish because adherence to a wet surface is difficult to achieve considering that the continual outward flow or leakage of dentinal fluid from the tubules while a filling or adhesive is setting is hard to stop.
Attempts to treat tooth sensitivity other than by plugging have involved depolarization of the nerve fiber membranes essential for nerve impulse transmission. Potassium salts, especially potassium nitrate, have been largely used for this purpose. For example, U.S. Pat. Nos. 4,751,072 and 4,631,185 describe using potassium bicarbonate and potassium chloride. U.S. Pat. No. 6,524,558 discloses an oral composition containing arginine and a calcium salt to treat dentinal hypersensitivity.
Arginine and other basic amino acids have been proposed for use in oral care and are believed to have significant benefits in combating cavity formation and tooth sensitivity. Combining these basic amino acids with minerals having oral care benefits, e.g., fluoride and calcium, to form an oral care product having acceptable long term stability, however, has proven challenging. In particular, the basic amino acid may raise the pH and facilitate dissociation of calcium ions that can react with fluoride ions to form an insoluble precipitate. Moreover, the higher pH has the potential to cause irritation. At neutral pH or acidic pH, however, a system utilizing arginine bicarbonate (which the art teaches is preferred) may release carbon dioxide, leading to bloating and bursting of the containers. Moreover, it might be expected that lowering the pH to neutral or acidic conditions would reduce the efficacy of the formulation because the arginine may form an insoluble arginine-calcium complex that has a poorer affinity for the tooth surface, and moreover that lowering the pH would reduce any effect the formulation might have on buffering cariogenic lactic acid in the mouth. Use of antimicrobial agents together with arginine and salts also have posed difficulties. Commercially available arginine-based toothpaste, such as ProClude® and DenClude®, for example, contain arginine bicarbonate and calcium carbonate, but not fluoride nor any antimicrobial agent.
Mouthwash and mouthrinse formulations also are well known in the art. Various formulations include antibacterial agents, flavorants, colorants, sweeteners, breath freshening agents, and the like. While a variety of agents can be included in rinse or wash formulations, their concurrent use may not be possible due to interactivity, adverse reactions among reactive agents, resulting in loss of activity. It would be desirable to provide a mouthwash or mouthrinse composition useful in the treatment of a variety of ailments, including for example, dentinal hypersensitivity, anticaries, bad breath, plaque formation, tartar control, stain prevention/whitening, dry mouth, erosion, gingivitis, etc.